Voyage To The Prehistoric Planet (1965)

aka's: Prehistoric Planet/Voyage To A Prehistoric Planet

In the year 2020, cosmonaut Marsha Evans (Faith Domergue) orbits the planet Venus while two astronauts and a robot journey on the surface. Professor Hartman (Basil Rathbone) is also on hand to observe the exploration from a distance. The explorers are then attacked by prehistoric beasts and then lose their robot (and nearly their lives) in a volcanic eruption that engulfs the planet. They later conclude that the Venusians were really human beings who destroyed their civilization with nuclear warfare.

Note: Most of the credits in the U.S. version of this film are phony in order to hide the fact that it was actually made in Russia.